Queen had just ended its four-year run with Paul Rodgers when, as May said, "The American Idol people asked us to come in and play on the final competition night. So it was between Adam and this other guy [Kris Allen]. ... They're both really good singers, but there's some kind of chemistry already between us and Adam. It was just instant."

"Just meeting them for the first time," Lambert said, "it was so surreal. I don't even think I realized the weight of that moment until after the fact."

Lambert finished in second place to Allen, but rumors about Lambert joining Queen started immediately following the show. A year and a half later, he sang a few songs with them at the MTV Europe Music Awards telecast and they cemented the relationship in the summer of 2012 with a small European tour. The new singer helped restore the band's fortunes, and they've toured the world several times over ever since.

May added, "It wasn't until this young man appeared -- not calling it a gift from God -- [but] we didn't ask for him, we didn't look for him, he just turned up. And he could do everything."

Lambert has repeatedly said that he's not looking to replace Freddie Mercury, but rather that his performance is a way of honoring Mercury's memory by keeping his songs alive. In the new documentary, he added that, since fronting Queen, he's found out "more about Freddie over the years and [learned] that there was definitely a loneliness there. I feel like I have enough in common with some of the things that Freddie was going through."

It's led to a period of growth for Lambert, as Taylor has noted. "When we very first met Adam," the drummer said, "he appeared to be more of a boy. I now see him as an incredibly accomplished man."

Lambert will return to Idol on Sunday as a guest celebrity mentor, working with each contestant on a Queen song. And he'll also appear on the May 19 season finale. Taylor will appear on Monday's episode of Good Morning America, and you can see them both in person later this year when they begin their Rhapsody tour.